[wasm] Grow reserved code space exponentially

If a new code allocation request cannot be fulfilled, do not just
reserve enough to fulfill this one request, but request at least 20
percent of the total reserved code space so far. This ensures that
the reserved space grows exponentially instead of linearly.

R=mstarzinger@chromium.org

Bug: chromium:987560
Change-Id: I3fc4dd0f7acee2a380495a87c0425c58058551bc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1718144Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62910}

src/wasm/wasm-code-manager.cc

@@ -480,8 +480,14 @@ Vector<byte> WasmCodeAllocator::AllocateForCode(NativeModule* native_module,
     Address hint = owned_code_space_.empty() ? kNullAddress
                                              : owned_code_space_.back().end();
 
+    // Reserve at least 20% of the total generated code size so far, and of
+    // course at least {size}. Round up to the next power of two.
+    size_t total_reserved = 0;
+    for (auto& vmem : owned_code_space_) total_reserved += vmem.size();
+    size_t reserve_size =
+        base::bits::RoundUpToPowerOfTwo(std::max(size, total_reserved / 5));
     VirtualMemory new_mem =
-        code_manager_->TryAllocate(size, reinterpret_cast<void*>(hint));
+        code_manager_->TryAllocate(reserve_size, reinterpret_cast<void*>(hint));
     if (!new_mem.IsReserved()) {
       V8::FatalProcessOutOfMemory(nullptr, "wasm code reservation");
       UNREACHABLE();